The present invention relates to a molding die for a synthetic resin molded foam, especially a synthetic resin molded foam having an open cell structure such as a flexible polyurethane molded foam. It also relates to a molding process for a synthetic resin molded foam using the molding die.
Conventionally, there has been proposed in Japanese Utility Model Laid-open No. 58-60418, a process of forming an interior member for a car such as a cushion pad by molding a polyurethane foam molding material while adjusting a pressure in a cavity portion.
The above process is configured in that a cavity for forming a molded product is formed between a lower mold and a core or an intermediate mold. An upper die is mounted to cover the lower die and the core for forming a pressure adjusting chamber (chamber portion) between the core and the upper die and vent holes for communicating the chamber portion to the cavity are formed in the core. Thus, air in the cavity is evacuated to the chamber portion through the vent holes.
In the process disclosed in Japanese Utility Model Laid-open No. 58-60418, since pressure between the cavity and the chamber portion is adjusted only through the vent holes, the sizes of the vent hole must be enlarged and/or the number of the vent holes must be increased, so that the air in the cavity is locally released. This causes problems in that the foaming balance of the foam is lost and considerable labor is required to clean burrs bitten into the vent holes after molding.
Further, in Japanese Patent Publication No. 7-102583, there is disclosed a process of molding a polyurethane foam molding material, comprising the steps of reducing a pressure in a cavity of a molding die, and pouring and foaming a polyurethane foam molding material containing 100 parts by weight of a polyol component and 0.1-0.6 part by weight of water as a foaming component, thereby fluidizing the material and filling the cavity with the material. In this process, the step of reducing a pressure of the cavity of the molding die is performed by evacuating the interior of the cavity through a gap between PL (parting line) surfaces formed when at least two-divided parts of the molding die are closed. More specifically, the interior of the cavity is evacuated through the gap between the PL surfaces by reducing a pressure in a space portion surrounding the PL surfaces of the molding die. As a result, the above process causes a problem that flashes bitten into the gap between the PL surfaces are liable to be formed on the molded foam.